In recent years, more and more electric loads are mounted in a vehicle. Since these electric loads consume more electric power, an electric power generator such as an alternator is required to generate more power while an internal combustion engine for driving a vehicle is in operation. The power generator is driven by a part of torque of the engine. Therefore, the engine torque used by the power generator increases, as the power generation of the power generator increases to meet the increased power consumption.
When the power generator uses a large engine torque in a short period of time, it is likely that the engine rotation speed reduces causing deceleration of the vehicle. In the worst case, this speed reduction may cause an engine stall and shutdown of power supply resulting in breakdown of various electric systems in the vehicle.
To counter this drawback, JP 7-23599A proposes to gradually change a command power (target power to be generated) of a power generator to suppress both a rapid torque change of the power generator and a rapid speed change of an internal combustion engine. However, if the power generation is thus changed only gradually in spite of necessity of an instantaneous or rapid change of the electric power; the electric power actually generated will largely deviate from a required electric power and a variation in a battery voltage becomes large. As a result, vehicle-mounted electric loads, which are operated with the battery power, cannot operate stably. For instance, electronic computers in the vehicle may operate erroneously due to insufficient power supply.